Process for producing sputtering target and sputtering target

ABSTRACT

A process for producing a sputtering target in which a target material is diffusion-bonded to a top face of a backing plate material, the process comprising: 
     a step of heating the top face of the target material by a hot plate while pressing from above thereby diffusion-bonding the target material to the backing plate material in such a manner that the step is performed at a center part prior to an outer peripheral part of the top face.

TECHNICAL FIELD

The present invention relates to a process for producing a sputteringtarget and a sputtering target.

BACKGROUND ART

Conventionally, as a process for producing a sputtering target, there isa process mentioned in JP 09-143707 A (Patent Document 1). In thisprocess for producing a sputtering target, hot isostatic pressingcapable of applying isotropic pressing (hot isotropic pressing process:hot isostatic press (HIP)) is applied to thereby diffusion-bond a targetmaterial to a backing plate material, thus producing a sputteringtarget.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP09-143707A1

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

It is an object of the present invention to provide a process forproducing a sputtering target that can increase a bonding strength of atarget material to a backing plate material (particularly, in a centerpart of the target material).

Means for Solving the Problems

To solve the above problem, the process for producing a sputteringtarget of the present invention is a process for producing a sputteringtarget in which a target material is diffusion-bonded to a top face of abacking plate material, which process includes heating a top face of thetarget material by a hot plate at a center part of the face prior to anouter peripheral part of the face while pressing from above to performdiffusion-bonding the target material to the backing plate material.

As used herein, the hot plate placed on the target material side duringpressing is sometimes referred to as “upper hot plate”, and the hotplate placed on the backing plate material during pressing is sometimesreferred to as “lower hot plate”. The diffusion bonding can be performedusing a hot press as mentioned later.

According to the process for producing a sputtering target of thepresent invention, the top face of the target material is heated by thehot plate at a center part of the face prior to an outer peripheral partof the face while pressing in the uniaxial direction to performdiffusion-bonding the target material to the backing plate material. Theprocess makes it possible to apply a load to the top face of the targetmaterial at least the center part of the face by the hot plate and toincrease the bonding strength of the center part of the target materialto the backing plate material.

According to the process of the present invention, the top face of thetarget material can be loaded by the hot plate in order from the centerpart to the outer peripheral part, thereby making it possible to removeair existing between the top face of the backing plate material and abottom face of the target material from the center part to the outerperipheral part. Therefore, a gap can be eliminated between the top faceof the backing plate material and the bottom face of the targetmaterial, and the bonding strength of the target material to the backingplate material can be increased.

According to the process of the present invention, owing to use of thehot press, reducing the pressure required for bonding, shortening thetime required for bonding and reducing the cost required for bonding canbe achieved, as compared with a hot isotropic pressing process.

In an embodiment of the process for producing a sputtering target, thecenter part of the top face of the target material projects upward fromthe outer peripheral part of the top face of the target material.

According to the embodiment, the center part of the top face of thetarget material projects upward from the outer peripheral part of thetop face of the target material so that, with a simple procedure, thetop face of the target material can be pressed by the hot plate at thecenter part of the face prior to the outer peripheral part of the faceduring boning.

According to an embodiment of the process for producing a sputteringtarget, in the hot plate, a center part of a press surface projectsdownward from an outer peripheral part of the press surface.

According to the embodiment, in the hot plate, the center part of thepress surface projects downward from the outer peripheral part of thepress surface so that, with a simple procedure, the top face of thetarget material can be pressed at the center part of the face prior tothe outer peripheral part of the face by the hot plate during bonding.

As used herein, the press surface means a surface in contact with thetarget material during pressing. Hereinafter, the press surface issometimes referred to as “bottom face of the hot plate”.

As used herein, the “top face of the target material” means a face ofthe target material, which is a face opposite to a face in contact withthe backing plate material during pressing.

In an embodiment of the process for producing a sputtering target, thetop face of the target material has a center part provided with aprojecting member projecting upward from the outer peripheral part ofthe top face.

According to the embodiment, the top face of the target material has acenter part provided with the projecting member projecting upward fromthe outer peripheral part of the top face so that, with a simpleprocedure, the top face of the target material can be pressed at thecenter part prior to the outer peripheral part of the top face by thehot press during bonding.

In an embodiment of the process for producing a sputtering target, thetarget material is incorporated inside a frame part of a backing platematerial having an annular frame part, and the top face of the targetmaterial is heated by the hot plate at the center part of the face priorto the outer peripheral part of the top face while pressing from above.

According to the embodiment, the target material is incorporated insidethe frame part of the backing plate material and the top face of thetarget material is heated by the hot plate at the center part of theface prior to the outer peripheral part of the top face while pressingfrom above.

This embodiment makes it possible to apply a load to the top face of thetarget material at the center part of the top face by the hot plate sothat bonding strength of the target material to the backing platematerial can be increased, even when the target material is incorporatedinside the frame part of the backing plate material.

In an embodiment, a sputtering target includes:

a backing plate material; and

a target material bonded to a top face of the backing plate material;

wherein a bonding strength between a center part of the target materialand the backing plate material is 7 kg/mm² or more.

In an embodiment, a bonded body for producing a sputtering target,includes:

a backing plate material; and

a target material bonded to a top face of the backing plate material;

wherein a bonding strength between a center part of the target materialand the backing plate material is 7 kg/mm² or more.

According to the embodiment, the bonding strength between the centerpart of the target material and the backing plate material is 7 kg/mm²or more so that the bonding strength of the target material to thebacking plate material can be increased.

Herein, the bonding strength between the center part of the targetmaterial and the backing plate material means, for example, the strengthof a bonding part with the backing plate material in a region where thetop face of the target material is projected, at the center part to beinitially pressed by a bottom face of the hot plate, against a bottomface of the target material when the top face of the target material ispressed at the center part of the face by the bottom face of the hotplate.

Effects of the Invention

According to the process for producing a sputtering target of thepresent invention, the top face of the target material is heated at thecenter part of the face prior to the outer peripheral part of the faceby the press surface of the hot plate while pressing from above toperform diffusion-bonding of the target material to the backing platematerial. The process makes it possible to increase the bonding strengthof the target material to the backing plate material (particularly, inthe center part of the target material).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 It is a perspective view showing a first embodiment of asputtering target of the present invention.

FIG. 2 It is a cross-sectional view of a sputtering target of a firstembodiment.

FIG. 3 It is an enlarged cross-sectional view of a sputtering target ofa first embodiment.

FIG. 4 It is an explanatory drawing explaining a process for producing asputtering target of a first embodiment.

FIG. 5 It is an explanatory drawing explaining a process for producing asputtering target of a first embodiment.

FIG. 6 It is an explanatory drawing explaining a process for producing asputtering target of a first embodiment.

FIG. 7 It is an explanatory drawing explaining a process for producing asputtering target of a first embodiment.

FIG. 8 It is a cross-sectional view of a sputtering target of a secondembodiment.

FIG. 9 It is a cross-sectional view of a sputtering target of a thirdembodiment.

FIG. 10 It is a cross-sectional view showing a sputtering target ofExamples 1 to 3.

FIG. 11 It is a cross sectional view showing a sputtering target ofExample 4.

FIG. 12 It is a cross-sectional view showing another mode of asputtering target of the present invention.

FIG. 13 It is a cross sectional view showing a further mode of asputtering target of the present invention.

FIG. 14 It is an explanatory view showing a position coordinate of abottom face (press surface) of an upper hot plate and a dimension of theposition coordinate.

MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail below with referenceto the embodiments shown in the drawings.

First Embodiment

FIG. 1 is a perspective view showing a first embodiment of a sputteringtarget of the present invention. FIG. 2 is a cross-sectional view of asputtering target. As shown in FIG. 1 and FIG. 2, a sputtering target 1includes a backing plate material 10 and a target material 20 bonded toa top face of the backing plate material 10. The backing plate material10 includes a base plate 11 and an annular frame part 12 provided alongan outer periphery of the top face of the base plate 11. The targetmaterial 20 is fit inside the frame part 12 of the backing platematerial 10 and is diffusion-bonded to the top face of the base plate11. A height direction of the frame part 12 is a vertical direction, aside of the base plate 11 is a bottom side, and a side opposite to thebase plate 11 is a top side. The backing plate material 10 and thetarget material 20 are formed into a circular shape when viewed fromabove. The backing plate material 10 and the target material 20 may beformed into an oval shape, an ellipse shape, a polygonal shape, or thelike.

The top face 21 of the target material 20 includes a sputtering face forreceiving an inert gas being plasmatized (or being ionized) duringsputtering. Target atoms contained in the target material 20 aresputtered out from the sputtering face with which the inert gas iscollided. The sputtered atoms are accumulated on a substrate arrangedfacing to the sputtering face to form a thin film on the substrate.

A center part of the top face 21 of the target material 20 projectsupward from an outer peripheral part of the top face 21 of the targetmaterial 20. The center part of the top face 21 includes a circularprojecting part 21 a projecting upwardly. The uppermost position of thetarget material 20 is higher than the uppermost position of the framepart 12 of the backing plate material 10 in a height direction of theframe part 12 of the backing plate material 10. In other words, the topface 21 of the target material 20 projects upward from a top face 12 aof the frame part 12 of the backing plate material 10.

The target material 20 can be produced from a material selected from thegroup consisting of metals such as aluminum (Al), copper (Cu), chrome(Cr), iron (Fe), tantalum (Ta), titanium (Ti), zirconium (Zr), tungsten(W), molybdenum (Mo), niobium (Nb), etc. and alloys thereof, but thematerial constituting the target material 20 is not limited thereto. Thematerial of the target material 20 is preferably a material which hashardness smaller than that of the backing plate material and is easilydeformed during diffusion bonding. Specifically, the material ispreferably Al or an Al alloy, and more preferably Al, and it isparticularly preferred to use Al in which a base material, except foradditive elements, has Al purity of 99.99% or more, more preferably99.999% or more, and still more preferably 99.9999% or more. When thepurity of Al increases, the hardness of the base material (targetmaterial) decreases, leading to deformation due to pressing so that thebondability with the backing plate material can further be enhanced.When Al is used as the target material, from the viewpoint of alloyspikes, electromigration, etc., Si, Cu, Nd, Mg, Fe, Ti, Mo, Ta, Nb, W,Ni, Co, and the like (preferably, Si, Cu, etc.) may be added as anadditive element. Preferably, an Al—Cu alloy (e.g., Al-1.0% Cu, Al-0.5%Cu, etc.), an Al—Si alloy (e.g., Al-1.0% Si, Al-0.5% Si, etc.), and anAl—Cu—Si alloy (e.g., Al-1.0% Si—0.5% Cu, etc.) are used. Al havingVickers hardness of 50 or less, preferably 45 or less, and morepreferably 40 or less are used.

The material of the backing plate material 10 may be the same as that ofthe target material 20. Preferably, the material of the backing platematerial 10 is a material selected from one or more of aluminum (Al),copper (Cu), titanium (Ti), tungsten (W), molybdenum (Mo), tantalum(Ta), niobium (Nb), iron (Fe), and alloys thereof, and more preferably amaterial selected from one or more of aluminum (Al), copper (Cu), andalloys thereof. Preferably, the hardness of the backing plate material10 is larger than the hardness of the target material 20. When thetarget material 20 is Al or an Al alloy, an A2024 alloy, purified Cu, aCu—Cr alloy, SUS304, an A5052 alloy, an A5083 alloy, an A6061 alloy, anA7075 alloy, and the like can preferably be used. Deformation of thebacking plate material can be suppressed by adjusting the Vickershardness to more than 50, preferably 100 or more, more preferably 110 ormore, and still more preferably 130 or more.

A diameter of the backing plate material 10 is, for example, 250 mm to850 mm, preferably 300 mm to 650 mm, and more preferably 350 mm to 550mm, and a diameter of the target material 20 is, for example, 200 mm to700 mm, preferably 250 mm to 600 mm, and more preferably 300 mm to 500mm, which are suitable as the backing plate material 10 and the targetmaterial 20 to be used for diffusion bonding. The diameter of thebacking plate material 10 and the diameter of the target material 20 arenot limited thereto but, from the viewpoint of work efficiency, theinside diameter of the frame material 12 of the backing plate material10, to which the target material 20 is incorporated, is preferably madelarger than the diameter of the target material 20 to be incorporated.When a distance between an outer periphery of the target material 20 andan inner periphery of the frame material 12 of the backing platematerial 10 is too large, the degree of deformation of the targetmaterial 20 generating in a direction other than a pressuring directionincreases, thus failing to obtain sufficient bonding strength or leadingto a change in crystallinity of the target material 20 easily.Therefore, the diameter of the inner periphery of the frame material 12of the backing plate material 10 is made larger than the target material20 to be incorporated by 0.1 mm to 10 mm, preferably 0.2 mm to 5 mm, andmore preferably 0.3 mm to 1 mm.

FIG. 3 is an enlarged view of FIG. 2. As shown in FIG. 3, a platinglayer 40 can be provided between the backing plate material 10 and thetarget material 20. The plating layer 40 thus provided enablesenhancement of bonding between the backing plate material 10 and thetarget material 20. More specifically, the plating layer 40 is providedat least between a top face 11 a of the base plate 11 and a bottom face20 a of the target material 20. The material of the plating layer 40 issilver, and may be metal such as chrome, zinc, copper, or nickel. Theplating layer 40 is formed in advance on at least one of the backingplate material 10 and target material 20 by a general plating processsuch as electrolytic plating or electroless plating. When producing alarge amount of sputtering target, it is generally preferred to use anelectrolytic plating process with high plating rate (as described inJPS58-55237A2, JP2010-222617A1, and JP2009-149965A1). When the platinglayer 40 is provided on the surface of the backing plate material 10 thetarget material 20, the surface may be provided with a layer of metalsuch as copper or zinc, as an underlying layer, by plating, followed byformation of a silver layer on the copper layer or the zinc layer byplating. At this time, the plating layer 40 includes a layer of metalsuch as copper or zinc, in addition to the silver layer. As mentionedabove, the plating layer 40 may be a single layer or multiple layers. Athickness of the plating layer 40 is usually from 5 μm to 200 μm,preferably from 10 μm to 100 μm, more preferably from 20 μm to 50 μm,and still more preferably from 25 μm to 40 μm. When the thickness of theplating layer is in the above range, bonding strength can maintainsufficient to suppress defective bonding such as occurrence of theunbonded portion.

FIG. 2 shows a sputtering target 1. The sputtering target 1 of FIG. 2may be a bonded body for producing a sputtering target. Thereafter, theframe part 12 of the backing plate material 10 and the top face 21 ofthe target material 20 of the bonded body for producing a sputteringtarget may be shaved off by machining using a milling machine, an NCmilling machine, a machining center, a lathe, an NC lathe, and the like,to obtain a sputtering target finished into a desired size and surfacestate.

A process for producing a sputtering target 1 will be described below.

As shown in FIG. 4, a metal material is cut using a milling machine, anNC milling machine, a machining center, a lathe, an NC lathe, and thelike to prepare a backing plate material 10 and a target material 20.Then, the backing plate material 10 and the target material 20 aresubjected to silver plating. At this time, a top face of the base plate11 and an inner peripheral surface of the frame part 12, and a bottomface and a side surface of the target material 20 (i.e., parts where thebacking plate material 10 and the target material 20 are in contact witheach other) are subjected to silver plating (plating layer 40 of FIG.3). Preferably, the top face of the base plate 11 and the bottom face ofthe target material 20 are provided with silver plating. The silverplating may be provided over the entire surface of the backing platematerial 10 and the target material 20 and, in this case, there is aneed to remove silver plating of the top face 21 (sputtering face) ofthe target material 20 in the final step. Treatments such as adegreasing treatment, an acid treatment, an alkali treatment, andrinsing may be performed as a pretreatment for providing a platinglayer, and these treatments can be performed by a known process. Whenthe material of the target material 20 and the backing plate material 10is Al or an Al alloy, a zincate treatment may be performed before theplating treatment because of a strong oxide film which is formed on theAl surface and which make it more difficult to perform a platingtreatment to the surface. The zincate treatment can be performed by aknown process and, for example, the materials are immersed in a zincatesolution containing sodium hydroxide and zinc oxide, and preferably azincate solution further containing a complexing agent and metal salt.The Al surface is substituted with Zn by the zincate treatment, thusenabling prevention or suppression of reoxidation of the activatedsurface. After the zincate treatment, immersion is performed in azincate peeling solution such as a nitric acid to thereby peel off azinc-substituted coating film, and the zincate treatment is performedagain so as to form a finer and uniform zinc-substituted coating film.The zincate treatment may be repeated three times or more. Beforeproviding a silver plating layer used for bonding, to prevent poorplating adhesion such as swelling and peeling of the plating layer, astrike plating treatment may be carried out using nickel, copper,silver, etc., and alloys containing these metals. For example, when thestrike plating treatment is performed using copper, a copper strikeplating layer can be formed by electrolytic plating in a platingsolution containing copper cyanide or copper phosphate.

Then, as shown in FIG. 5, the target material 20 is incorporated insidethe frame part 12 of the backing plate material 10. This is called anincorporating step. At this time, as shown in FIG. 6, the center part(projecting part 21 a) of the top face 21 of the target material 20projects upward from the outer peripheral part of the top face 21. Theuppermost position of the target material 20 is set to be higher thanthe uppermost position of the frame part 12 of the backing platematerial 10 in the height direction of the frame part 12 of the backingplate material 10. The uppermost position of the target material 20 isthe position of the projecting part 21 a formed on the top face 21 ofthe target material 20. The uppermost position of the frame part 12 ofthe backing plate material 10 is the position of the top face 12 a ofthe frame part 12.

After the incorporating step, as shown in FIG. 7, the target material 20is diffusion-bonded to the backing plate material 10. This is called abonding step. At this time, the backing plate material 10 and the targetmaterial 20 are sandwiched from the upper and lower sides by the upperheating plate 31 and the lower heating plate 32, heated and then pressedin the vertical direction. This is called hot pressing. Namely, thebacking plate material 10 and the target material 20 are bonded via theplating layer.

The bonding step shown in FIG. 7 will be described more specifically.The top face 21 of the target material 20 is heated at the center part(projecting part 21 a) of the face prior to the outer peripheral part ofthe face by a bottom face 310 of the upper hot plate 31 while pressingfrom above, to perform diffusion-bonding of the target material 20 tothe backing plate material 10. In the step, the bottom face 310 of theupper hot plate 31 is flat, but the center part (projecting part 21 a)of the top face 21 of the target material 20 projects upward from theouter peripheral part of the top face 21 so that, with a simplestructure, the top face 21 of the target material 20 can be pressed atthe center part (projecting part 21 a) of the top face prior to theouter peripheral part of the face by the upper hot plate 31. The shapeof the projecting part 21 a is composed of a single ramp but may becomposed of a plurality of ramps, i.e., more than two ramps as shown inFIG. 10. A top face of the projecting part 21 a is flat or may have aconvex curved surface. When the top face of the projecting part 21 a hasa convex curved surface, a region of the projecting part 21 a in contactwith the bottom face 310 of the upper hot plate 31 and pressed duringpressing by the bottom face 310 of the upper hot plate 31 can beregarded as the center part of the top face 21 of the target material20.

A width of the projecting part 21 a usually accounts for 30% or more ofa width (diameter) of the target material, and preferably 40 to 60% soas to increase the bonding strength in the center part of the targetmaterial 20. The degree of projection from the top surface 21 of theprojecting part 21 a can be judged by an angle, which is formed by aline segment connecting an outer peripheral end edge of the outerperipheral part of the top face 21 and an outer peripheral end edge ofthe projecting part 21 a, and the outer peripheral part of the top face21 in a vertical section of the target material 20. The angle formed bythe above-mentioned line segment and the outer peripheral part of thetop face 21 is preferably 0.050 or more, more preferably 0.050 to 0.500,and still more preferably 0.100 to 0.300. When the angle is in the aboverange, the pressure from the upper hot plate 31 can be effectivelytransferred to the target material 20 or the backing plate material 10so that bonding strength can be increased. When an upper section of theprojecting part 21 a is composed of multiple ramps of two or more ramps,as shown in FIG. 10, the maximum angle among the angles, which is formedby the line segment connecting the outer peripheral end edge of theouter peripheral part of the top face 21 and the outer peripheral endedge of each ramp of the projecting part, and the outer peripheral partof the top face 21, may be in the above range. When the shape of theprojecting part 21 a is a convex curved surface, the maximum angle amongthe angles, formed by the line segment in contact with the convex curvessurface and the outer peripheral part of the top face 21, may be in theabove range.

Hot pressing can be performed using a known hot press machine. Thesputtering target and the bonded body for producing a sputtering targetof the present invention can be manufactured by a process including abonding step other than those in the above embodiments. For example, inthe bonding step shown in FIG. 7, when pressing the backing platematerial 10 and the target material 20 in the vertical direction, onlythe upper hot plate 31 may be pressed downward in a state where thelower hot plate 32 is fixed. Alternatively, only the lower hot plate 32may be pressed upward in a state where the upper hot plate 31 is fixed.The pressing direction is not necessarily required to be the verticaldirection as long as an assembly composed of the backing plate material10 and the target material 20 can be fixed so as not to interfere withbonding, and the backing plate material 10 and the target material 20may be placed in parallel with the vertical direction and bonded bypressing in the horizontal direction. To uniformly bond without formingthe unbonded portion, bonding is performed by pressing in the verticaldirection. FIG. 7 shows an example of a process for installing anassembled body in which the target material 20 is incorporated insidethe backing plate material 10 on the hot plate. However, the targetmaterial 20 may be placed on a top side (the top face 21 of the targetmaterial 20 is in contact with the upper hot plate 31) or may be placedon a bottom side (the top face 21 of the target material 20 is incontact with the lower hot plate 32). In this step, a surface of the hotplate that is in contact with the top face 21 of the target material 20can be called a press surface.

An example of the conditions for hot pressing will be described below.The hot pressing step include a preheating step of preheating anassembled body in which a target material 20 is incorporated inside abacking plate material 10, and a subsequent pressing step. When the sizeof the target material is φ⁴⁵⁰ mm, the temperature of the hot plateduring hot pressing depends on the composition of the target material,and is 200° C. to 500° C., preferably 220° C. to 400°±10° C., and morepreferably 230° C. to 330° C. Preferably, preheat is conducted in such amanner that the temperature of the target material is ±20° C., andpreferably ±10° C., of the temperature of the hot plate. The temperatureof the hot plate during preheating is 190° C. to 500° C., preferably210° C. to 400° C., and more preferably 220° C. to 370° C., and thepreheating time is 5 minutes or more, preferably 5 minutes to 60minutes, and more preferably 10 minutes to 30 minutes. An example of thepreheating process includes a process which include a step of placing,on the lower hot plate, the target material 20 incorporated inside thebacking plate material 10, and statically placing the upper hot plate ina state of being close to the top face of the target material of theassembly, i.e. immediately above the top face 21 of the target materialof the assembly, a position which is preferably from 0 mm to 50 mm, morepreferably from 10 mm to 40 mm, and still more preferably from 15 mm to30 mm, away from the top face. The pressure to be applied to theassembled body in which the target material 20 is incorporated insidethe backing plate material 10 during hot pressing is 8 MPa or more,preferably from 10 MPa to 80 MPa, and more preferably 25 MPa to 70 MPa,and the pressing time is 10 minutes or more, preferably from 10 minutesto 60 minutes, and more preferably from 20 minutes to 40 minutes. Whenthe size of the target material increases, the pressure to be appliedalso increases.

The material constituting the upper hot plate 31 and the lower hot plate32 is preferably a high strength alloy such as an alloy steel or acarbon steel. For example, chromium molybdenum steels such as SCM430 andSCM440, stainless steels such as SUS304 and SUS316, and carbon steelssuch as S45C and S60C can be used.

There is no particular limitation on the shape of the upper hot plate 31and the lower hot plate 32, and the surface, against which the targetmaterial is pressed, may have a circular, rectangular, squarequadrangular, or other polygonal shape. The size of the upper hot plate31 and the lower hot plate 32 may be any size as long as it enablespressing the entire target material 20, and the size may be determinedin accordance with the size of the target material 20. For example, topress a target material having a size of φ450 mm and a backing platematerial having a size of φ550 mm, the size of 1,000 mm×1,000 mm×t100 mmcan be used in the case of a square hot plate. The size of the hot plateon the side in contact with the backing plate material 10 may besubstantially equal to or larger than the size of the backing platematerial. Regarding the size of the hot plate on the side in contactwith the upper surface 21 of the target material 20, the length of oneside of the pressing surface is 0.8 to 5 times, preferably 1 to 3 times,and more preferably 1.2 to 2.5 times the size of the target material.

According to a first embodiment, a sputtering target 1 as shown in FIG.2 is produced. In the sputtering target 1, the bonding strength betweenthe center part of the bottom face of the target material 20 and thebacking plate material 10 becomes 7 kg/mm² or more so that bondingstrength can be increase. The bonding strength between the center partof the target material 20 and the backing plate material 10 means thestrength of the bonding part with the backing plate material 10 in aregion where the top face 21 of the target material 20 can be pressed atthe center part (that means a region which is in contact with the bottomface 310 and pressed when the projecting part 21 or the top face of theprojecting part 21 is a convex curved surface) to be initially by thebottom face 310 is projected against the bottom face of the targetmaterial 20. The bonding strength between the center part of the targetmaterial 20 and the backing plate 10 according to the process of thepresent application is usually 15 kg/mm² or less. At least a part of theframe part 12 of the backing plate material 10 may be removed by finishcutting after bonding the target material 20 to the backing platematerial 10, and the top face 21 or the projecting part 21 a of thetarget material 20 may be smoothed by polishing. Preferably, a millingmachine, an NC milling machine, a machining center, a lathe, an NClathe, and the like can be used for finish cutting of the sputteringtarget 1.

According to the process for producing the sputtering target 1, the topface 21 of the target material 20 is heated at the center part of theface prior to the outer peripheral part of the face by the press surface310 of the upper hot plate 31 while pressing from above to therebyperform diffusion-bonding of the target material 20 to the backing platematerial 10.

According to a conventional process, repetition of bonding by the hotpress sometimes makes the center part of the upper hot plate 31 slightlydeformed and recessed. Since the target material 20 is fit inside theframe part 12 of the backing plate material 21, followed by beingpressed, the pressure at bonding tends to concentrate on the outerperipheral part of the target material 20, so that the bonding strengthcannot sufficiently be increased at the center part of the targetmaterial 20.

According to the present embodiment, the top face 21 of the targetmaterial 20 can be loaded at the center part of the face by the upperhot plate 31 so that bonding strength of the target material 20 to thebacking plate material 10 can be increased. Particularly, the bondingstrength can be increased at the center part of the target material 20where only low bonding strength could be obtained by a conventionalprocess.

According to the first embodiment, the top face 21 of the targetmaterial 20 can be loaded in order from the center part to the outerperipheral part by the upper hot plate 31, to thereby remove airexisting between the top face of the backing plate material 10 and thebottom face of the target material 20 from the center part to the outerperipheral part. Therefore, a gap can be eliminated between the top faceof the backing plate material 10 and the bottom face of the targetmaterial 20, thus enabling an increase in bonding strength of the targetmaterial 20 to the backing plate material 10.

According to the first embodiment, owing to use of the hot press,reducing the pressure required for bonding, shortening the time requiredfor bonding and reducing the cost required for bonding can be achievedas compared with the hot isotropic pressing process.

According to the first embodiment, even when the target material 20 isincorporated inside the frame part 12 of the backing plate material 10,the top face 21 of the target material 20 can be loaded even at thecenter part of the face by the upper hot plate 31 to thereby increasebonding strength of the target material 20 to the backing plate material10.

According to the first embodiment, the backing plate material 10 and thetarget material 20 are bonded together through the plating layer 40 sothat the backing plate material 10 and the target material 20 can becertainly bonded together even at a temperature lower than a temperaturein the case where the plating layer 40 is not provided, for example,200° C. to 500° C., preferably 220° C. to 400° C., and more preferably230° C. to 330° C. with bonding by pressing from the uniaxial direction,preferably from above (uniaxial press). Particularly, when the targetmaterial 20 is made of a relatively low melting metal such as Al and anAl alloy, bonding can be achieved at the above-mentioned low temperaturevia the plating layer to thereby suppress deterioration (change incrystallinity) of the target material 20.

According to the first embodiment, the top face 11 a of the base plate11 of the backing plate material 10 and the bottom face 20 a of thetarget material 20 are preferably bonded together through the platinglayer 40. By hot pressing, a force can be transmitted to the top face 11a of the backing plate material 10 and the bottom face 20 a of thetarget material 20 without resistance and adhesion at the bondingsurface can be increased, leading to an increase in bonding strength.Since the hot pressing is uniaxial pressing, there is no need to apply aforce that enables bonding to a side surface of the target material 20and an inner peripheral surface of the frame part 12 of the backingplate material 10, and there is no need to bond the side surface of thetarget material 20 to the backing plate material 10.

If the side surface of the target material 20 is not bonded to thebacking plate 10, the frame part of the backing plate can be cut at aroot thereof in a circumference direction to thereby reduce cutting timein the case of performing finishing to obtain a sputtering target havinga backing plate shape in which the bonding surface side or the framepart remains slightly flat.

Second Embodiment

FIG. 8 is a cross-sectional view showing the second embodiment of aprocess for producing a sputtering target of the present invention. Thesecond embodiment differs from the first embodiment in a shape of atarget material and an upper hot plate. This difference in elements willbe described below.

As shown in FIG. 8, in a sputtering target 1A before bonding, a top face21 of a target material 20A has a flat surface. A center part of a presssurface 310 of an upper hot plate 31A projects downward from an outerperipheral part of the press surface 310. In other words, the centerpart of the press surface 310 has a projecting part 310 a projectingdownwardly. A shape of the projecting part 310 a is composed of a singleramp but may be composed of multiple ramps. The press surface of theprojecting part 310 a is flat but may have a convex curved surface.

A width of the projecting part 310 a usually accounts for 30% or more ofa width (diameter) of the target material, and preferably 40 to 60% soas to increase the bonding strength in the center part of the targetmaterial 20.

In the embodiment shown in FIG. 8, the center part of the press surface310 of the upper hot plate 31A projects downward from the outerperipheral part of the press surface 310 so that the top face 21 of thetarget material 20A can be pressed at the center part of the face priorto the outer peripheral part of the face during bonding the upper hotplate 31A with a simple procedure. The second embodiment has an elementidentical to the first embodiment except for the above difference.

Third Embodiment

FIG. 9 is a cross-sectional view showing a third embodiment of a processfor producing a sputtering target of the present invention. The thirdembodiment differs from the first embodiment in a shape of a targetmaterial. The difference in an element will be described below.

As shown in FIG. 9, in a sputtering target 1B before bonding, the topface 21 of the target material 20A is flat. A center part of the topface 21 of the target material is provided with a projecting member 41projecting upward from the outer peripheral part of the top face 21 ofthe target material 20A. The projecting member 41 is composed of, forexample, a heat-resistant sheet made of a resin such as polyimide or ametal sheet free from diffusion-bonding. The projecting member 41 iscomposed of a single sheet but may be composed of multiple sheets eachhaving a different diameter.

A width of the projecting member 41 usually accounts for 30% or more ofa width (diameter) of a target material, and preferably 40 to 60% so asto increase the bonding strength in the center part of a target material20A. The degree of projection from the top surface 21 of the targetmaterial 20A of the projecting member 41 can be judged by an angle in avertical section of the target material 20A, which angle is formed by aline segment connecting an outer peripheral end edge of the outerperipheral part of the top face 21 and an outer peripheral end edge ofthe projecting member 41, and the outer peripheral part of the top face21. The angle formed by the above-mentioned line segment and the outerperipheral part of the top face 21 is preferably 0.050 or more, morepreferably 0.05° to 0.50°, and still more preferably 0.10° to 0.30°.When the angle is in the above range, the pressure from the upper hotplate 31 can effectively be transferred to the target material 20A andthe backing plate material 10, to thereby increase bonding strength.When the projecting material 41 is composed of multiple differentsheets, the maximum angle among the angles, which is formed by the linesegment connecting the outer peripheral end edge of the outer peripheralpart of the top face 21 and the outer peripheral end edge of eachprojecting member 41, and the outer peripheral part of the top face 21,may be in the above range.

In the embodiment shown in FIG. 9, the projecting member 41 projectingupward from the outer peripheral part of the top face 21 is provided atthe center part of the top face 21 of the target material 20A, so thatthe center part of the top face 21 of the target material 20A can bepressed at the center part of the face prior to the outer peripheralpart of the top face 21 of the target material 20A during bonding by theupper hot plate 31A, with a simple procedure. The third embodiment haselements identical to the first embodiment except for the abovedifference.

The present invention is not limited to the above embodiments, butdesign can be changed without departing from the spirit and scope of thepresent invention. For example, features of the first to thirdembodiments may be used in combination in various ways.

In the above embodiment, the backing plate material includes the framepart, which may be omitted or may be removed by finish-cutting afterdiffusion-bonding.

Further, in the embodiment, the target material 20 is pressed by theupper hot plate for hot pressing in order from the center part to theouter peripheral part of the target material 20 to thereby deform in acontact part with the backing plate material 10 from the center part tothe outer peripheral part. Therefore, inside the frame part 12, thebonding strength with the backing plate material 10 tends to be slightlyhigher in the outer peripheral part than the center part of the targetmaterial 20 due to a deformation force from the center part and pressureapplied from the upper hot plate. Usually, a difference in the bondingstrength between the outer peripheral part and the center part is 0.1kg/mm² or more, and preferably from 0.1 kg/mm² to 3 kg/mm². When theframe part 12 is removed by finish cutting after bonding, defects mightoccur at a bonding surface between the backing plate material 10 and theframe part 12 due to a force applied to the frame part 12 and the outerperipheral part of the target material 20 during cutting. However, whena difference in the bonding strength between the outer peripheral partand the center part is in the above range, the bonding strength of theouter peripheral part is slightly higher than that of the center part tothereby suppress the occurrence of defects in the bonding surface duringfinish cutting.

EXAMPLES

The present invention will be described by way of Examples 1 to 4 andComparative Example.

The sputtering targets of Examples 1 to 3 are sputtering targets shownin FIG. 6. The sputtering target before bonding includes the firstprojecting part 21 a in the center part of the top face 21 of the targetmaterial 20.

The maximum width W1 of the projecting part 21 a is a diameter of thefirst projecting part 21 a. The maximum height H of the projecting part21 a is a height from the outer peripheral part of the top face 21 tothe first projecting part 21 a. The maximum angle θ of the projectingpart 21 a is the maximum angle among the angles, which is formed by theline segment connecting the outer peripheral end edge of the outerperipheral part of the top face 21 and the outer peripheral end edge ofthe first projecting part 21 a and the outer peripheral part of the topface 21 in a vertical cross section of the target material 20B. A targetwidth W2 is a diameter of the target material 20.

In Example 1, the maximum width W1 was 220 mm, the maximum height H was0.3 mm, the maximum angle θ was 0.150, and a ratio of the maximum widthW1 to the target width W2 was 49%. In Example 2, the maximum width W1was 260 mm, the maximum height H was 0.3 mm, an angle θ was 0.180, and aratio of the maximum width W1 to the target width W2 was 58%. In Example3, the maximum width W1 was 180 mm, the maximum height H was 0.3 mm, anangle θ was 0.130, and a ratio of the maximum width W1 to the targetwidth W2 was 40%.

A sputtering target of Example 4 is a sputtering target 1D shown in FIG.11. The sputtering target 1D before bonding was provided with the firstto the fourth members 41 a to 41 d in this order in the center part ofthe top face 21 of the target material 20A. Each diameter of the firstto the fourth members 41 a to 41 d increased in order. The diameter ofthe first projecting member 41 a was 30 mm, the diameter of the secondprojecting member 41 b was 50 mm, the diameter of the third projectingmember 41 c was 100 mm, and the diameter of the fourth projecting member41 d was 260 mm. Each thickness of the first to the fourth projectingmembers 41 a to 41 d was 0.1 mm.

The maximum width W1 of the projecting members 41 a to 41 d is adiameter of the fourth projecting member 41 d. The maximum height H ofthe projecting members 41 a to 41 d is a height from the outerperipheral part of the top face 21 to the fourth projecting member 41 d.The maximum angle θ of the projecting members 41 a to 41 d indicates themaximum angle among the angles, which is formed by a line segmentconnecting the outer peripheral end edge of the outer peripheral part ofthe top face 21 and an outer peripheral end edge of each of the fourthprojecting members 41 a to 41 d and the outer peripheral part of the topface 21 in a vertical section of the target material 20A. The targetwidth W2 is a diameter of a target material 20B.

In Example 4, the maximum width W1 was 260 mm, the maximum height H was0.4 mm, the maximum angle θ was 0.240, and a ratio of the maximum widthW1 to the target width W2 was 58%.

In a sputtering target of Comparative Example, a target material had aflat top face, and there are neither projecting parts 21 a, 21 b shownin FIG. 10 nor projecting members 41 a to 41 d shown in FIG. 11.

In Examples 1 to 4 and Comparative Example, the top face of the targetmaterial was pressed by the upper hot plate 31 having a flat presssurface 310 (see FIG. 7), thereby diffusion-bonding the target materialto the backing plate material. Al-0.5% Cu having a size of φ450 mm×t14.5mm was used as the target material, and a A2024 alloy having a size ofφ550 mm×t25 mm provided with a recess part having a size of φ450.3 mm×12mm in depth was used as the backing plate material. A polyimide film wasused as the projecting members 41 a to 41 d of Example 4. A silverplating layer was provided between the target material and the backingplate material, followed by diffusion-bonding under the conditions of apressure of 56 MPa, a bonding temperature of 270° C., a preheating timeof 10 minutes, and a pressing time of 30 minutes. The silver platingtreatment was applied to bonding surface side of the target material andthe backing plate material, followed by a zincate treatment and a copperstrike plating and further formation of a silver plating layer having athickness of about 10 μm on the bonding surfaces of both target materialand backing plate material by an electrolytic plating process. In hotpressing, a hot press machine was used. The hot press machine was amachine (model number: MSF-1000HP) manufactured by MORI IRON WORKS CO.,LTD. equipped with an upper hot plate and a lower hot plate, and eachmade of SCM440 and has a size of 1,000 mm×1,000 mm×t100 mm. An assembledbody composed of a backing plate material and a target material placedon a lower hot plate was heated while moving an upper hot plate in avertically downward direction and pressing from above. The bondingstrength was measured using a test piece sampled from a sputteringtarget obtained by the diffusion-bonding. A section having a size of 10mm in width×15 mm in depth×23 mm in height was cut out from thesputtering target and then a neck was formed in a vertical directionwith the bonding surface as the center such that the section has a sizeof 4 mm in width×15 mm in depth (an area of the bonding has a size of 4mm in width×15 mm in depth) to obtain a tensile test piece for measuringthe bonding strength. Using a universal testing machine (UH-500kNIR,manufactured by Shimadzu Corporation), the bonding strength was measuredby applying a load in a direction perpendicular to the bonding surface.The results are shown in Table 1. The bonding strength of the centerpart mentioned in Table 1 was determined using the tensile test piececut out from the inside of the maximum width W1 in the projecting partof the top face of the target material, while the bonding strength ofthe outer peripheral part mentioned in Table 1 was determined using thetensile test piece cut out from the outside of the maximum width W1 inthe projecting part of the top face of the target material.

In the sputtering target obtained by diffusion-bonding in Examples 1 to4, the top face of the target material was smoothened by removing andshaving off the frame part of the backing plate material by finishcutting using an NC milling machine.

TABLE 1 Ratio of Bonding strength Thickness of plating Maximum Maximummaximum width kg/mm² layer (μm) width height W1/target width MaximumCenter Outer peripheral Center Outer W1 (nm) H (mm) W2 (%) angle θ (°)part part part peripheral part Comparative — — 0 0 0 14.6 28.0 30.2Example Example 1 220 0.3 49 0.15 8.3 9.5 12.6 15.2 Example 2 260 0.3 580.18 9.7 9.9 15.6 16.1 Example 3 180 0.3 40 0.13 9.5 11.2 15.2 19.6Example 4 260 0.4 58 0.24 7.4 10.3 11.0 17.1

As is apparent from Table 1, the bonding strength of the center partbetween the target material and the backing plate material was 0[kg/mm²] in Comparative Example, while 7.4 to 9.7 [kg/mm²] in Examples 1to 4. In Examples 1 to 4, there was no problem in the bonding strengthbetween the target material and the outer peripheral part of the backingplate material. Therefore, the strength of the outer peripheral part wasappropriately adjusted to increase the bonding strength of the centerpart in Examples 1 to 4, as compared with Comparative Example. Asmentioned above, the entire bonding strength was increased by pressingthe top face of the target material by the upper hot plate at the centerpart of the face prior to the outer peripheral part of the face.

In the sputtering targets obtained in Examples 1 to 4, finish cuttingwas performed to remove the frame part of the backing plate material andpolish the top face of the target material. After finishing, problemssuch as defects in the bonding part between the target material and thebacking plate were not confirmed even in the outer peripheral part towhich a strong force would be applied.

Table 1 shows a thickness (total thickness of a plating layer betweenthe target material and the backing plate material in thediffusion-bonded sputtering target) of the plating layer of Examples 1to 4 and Comparative Example. In Examples, the plating layer is a layercontaining Ag as a main component. As shown in Table 1, in Examples 1 to4, there is a relationship between the thickness of the plating layerand the bonding strength, and it is apparent that the bonding strengthbecomes higher as the plating layer becomes thicker. Meanwhile, inComparative Example, satisfactory pressing cannot be performed becauseof a flat top face of the target material, so that the bonding strengthis 0 kg/mm², and there is no relationship with the thickness of theplating layer.

Description will be made of a mechanism of a change of bonding strengthaccording to the thickness of the plating layer. It is considered that,in the vicinity of the bonding surface between the target material andthe plating layer, metal contained in the target material and metalcontained in the underlaying layer of the plating layer diffuse to forma plating layer having high impurity concentration. Therefore, it isconsidered that an increase in the thickness of the plating layer leadsto an increase in purity of Ag in the center part of the plating layerand a decrease in amount of impurities in the vicinity of the bondingsurface, thus increasing the bonding strength. The tension strength ofAl-0.5% Cu itself is about 7 kg/mm² and the tension strength of Agitself of 4N is about 16 kg/mm². The thickness of the plating layer maybe increased, but an influence by physical properties of Ag issaturated. Since Ag is expensive metal and excessive thickness leads toan increase in cost.

In the above embodiments, the projecting part of the top face of thetarget material has a ramp shape but may have other shapes. For example,as shown in FIG. 12, the shape of a top face 21 of a target material 20Cmay be a curved surface in which the center part projects upward from anouter peripheral part. As shown in FIG. 13, a projecting part 21 a of atop face 21 of a target material 20D may have a shape of a curvedsurface in which the center part projects upward from an outerperipheral part.

Likewise, the bottom face of the upper hot plate may also have a shapeof a curved surface in which center part projects upward from the outerperipheral part. The shape of the projecting part of the bottom face ofthe upper hot plate may also have a curved surface in which the centerpart projects upward from the outer peripheral part.

When the press surface of the upper hot plate has shape of a curvedsurface, the dimension of the press surface of the upper hot plate maybe the dimension shown in FIG. 14. FIG. 14 shows a positional coordinatein which the press surface of the upper hot plate is divided into A to Ein a lateral direction and into 1 to 5 in a longitudinal direction, andshows the dimension of the positional coordinate. A unit of thedimension is mm and the positive value of the dimension indicates aprojecting state. The length for dividing in the longitudinal directionand the lateral direction is 200 mm. As is apparent from FIG. 14, thecenter of the press surface of the upper hot plate (position of “C” inthe lateral direction and the position of “3” in the longitudinaldirection) has the uppermost height, e.g., +0.4 mm, and the heightgradually decreases toward the outer periphery of the press surface ofthe upper hot plate.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1, 1A to 1F Sputtering target    -   10 Backing plate material    -   11 Base plate    -   11 a Top face    -   12 Frame part    -   12 a Top face    -   20, 20A to 20D Target material    -   20 a Bottom face    -   21 Top face    -   21 a Projecting part    -   21 b Projecting part    -   31, 31A Upper hot plate    -   310 Bottom face (press surface)    -   310 a Projecting part    -   32 Lower hot plate    -   40 Plating layer    -   41 Projecting member    -   41 a to 41 d First to fourth projecting member

1. A process for producing a sputtering target in which a targetmaterial is diffusion-bonded to a top face of a backing plate material,which process comprises heating the top face of the target material by ahot plate at a center part prior to an outer peripheral part of the topface while pressing from above to perform diffusion-bonding of thetarget material to the backing plate material, said target materialhaving hardness smaller than the backing plate material.
 2. The processfor producing a sputtering target according to claim 1, wherein thecenter part of the top face of the target material projects upward fromthe outer peripheral part of the top face.
 3. The process for producinga sputtering target according to claim 1, wherein, in the hot plate, thecenter part of a press surface in contact with the target materialduring pressing projects downward from an outer peripheral part of thepress surface.
 4. The process for producing a sputtering targetaccording to claim 1, wherein the center part of the top face of thetarget material is provided with a projecting member projecting upwardfrom the outer peripheral part of the top face of the target material.5. The process for producing a sputtering target according to claim 1,further comprising: incorporating the target material inside a framepart of a backing plate material having an annular frame part, followedby heating the top face of the target material by a hot plate at acenter part prior to an outer peripheral part of the top face whilepressing from above to perform diffusion-bonding of the target materialto the backing plate material.
 6. A sputtering target, comprising: abacking plate material; and a target material bonded on a top face ofthe backing plate material; said target material having hardness smallerthan the backing plate material, wherein a bonding strength between acenter part of the target material and the backing plate material is 7kg/mm² or more, the backing plate material has a bonding strength higherin the outer peripheral part than in the center part of the targetmaterial, and a difference in a bonding strength between an outerperipheral part and the center part is from 0.1 kg/mm² to 3 kg/mm².
 7. Abonded body for producing a sputtering target, comprising: a backingplate material; and a target material bonded on a top face of thebacking plate material, wherein the target material has hardness smallerthan the backing plate material, a bonding strength between a centerpart of the target material and the backing plate material is 7 kg/mm²or more, the backing plate material has a bonding strength higher in theouter peripheral part than in the center part of the target material,and a difference in a bonding strength between an outer peripheral partand the center part is from 0.1 kg/mm² to 3 kg/mm².
 8. A process forproducing a sputtering target in which a target material isdiffusion-bonded to a top face of a backing plate material, whichprocess comprises heating the target material by a hot plate at a centerpart of an opposite face to a face in contact with the backing platematerial prior to an outer peripheral part of the opposite face whilepressing from the uniaxial direction to perform diffusion-bonding of thetarget material to the backing plate material, said target materialhaving hardness smaller than the backing plate material.
 9. The processfor producing a sputtering target according to claim 8, wherein thecenter part of the opposite face of the target material projects upwardfrom the outer peripheral part of the opposite face.
 10. The process forproducing a sputtering target according to claim 8, wherein, in the hotplate, the center part of a press surface in contact with the targetmaterial during pressing projects downward from an outer peripheral partof the press surface.
 11. The process for producing a sputtering targetaccording to claim 8, wherein the center part of the opposite face ofthe target material is provided with a projecting member projectingupward from the outer peripheral part of the opposite face of the targetmaterial to a face opposite to a face in contact with the backing plate.12. The process for producing a sputtering target according to claim 8,further comprising: incorporating the target material inside a framepart of a backing plate material having an annular frame part, followedby heating the target material by the hot plate at the center part of anopposite face to a face in contact with the backing plate material priorto the outer peripheral part of the opposite face while pressing fromthe uniaxial direction to perform diffusion-bonding of the targetmaterial to the backing plate material.